The objective of this research is to provide new comparative data on temporal processing capabilities of relatively simple vertebrate auditory systems. Fish species known to differ in he anatomy of their peripheral auditory system as well as in their bioacoustic behavior will be studied to determine if there are any differences in the temporal processing capabilities of fish auditory systems. Psychophysical studies employing operant conditioning techniques and sound stimuli consisting of (1) amplitude-modulated signals and (2) pulse trains of filtered clicks and gated noises will be used to focus on aspects of temporal processing that appear to be biologically significant, such as th ability of some fish to respond differentially to species-specific sounds on the basis of systems to (1) amplitude fluctuations (2) different pulse train periodicities and (3) changes in periodicities will be measured for a variety of conditions. These measurements will provide a comparative description of temporal processing capabilities among fishes and will test the hypotheses that (1) there are interspecific differences in temporal tuned mechanisms inthe fish auditory system and (3) differences in temporal "tuning" characteristics may underly the abilities of some fish to recognize species-specific sounds.